Bleach activators are important ingredients in detergents, scouring salts and dishwashing agents. They permit a bleaching action even at relatively low temperatures in that they react with hydrogen peroxidexe2x80x94usually perborates or percarbonatesxe2x80x94to release an organic peroxycarboxylic acid.
The bleaching result obtainable depends on the nature and reactivity of the peroxycarboxylic acid formed, on the structure of the bond that is to be perhydrolyzed and on the solubility of the bleach activator in water. Since the activator is usually a reactive ester or an amide, it is frequently necessary to use it in granulated form for the intended application in order to prevent hydrolysis in the presence of alkaline detergent ingredients and to ensure an adequate shelf life.
Numerous auxiliaries and processes have been proposed in the past for granulating these substances. EP-A-0 037 026 describes a process for producing readily soluble activator granules comprising 90 to 98% activator with 10 to 2% cellulose ethers, starch or starch ethers. Granules consisting of bleach activator, film-forming polymers and added organic C3-C6-carboxylic, hydroxycarboxylic or ether carboxylic acid are specified in WO 90/01535. EP-A-0 468 824 discloses granules comprising bleach activator and a film-forming polymer which is more soluble at a pH of 10 than at a pH of 7 DE-A-44 39 039 describes a process for producing activator granules by mixing a dry bleach activator with a dry, inorganic binder material containing water of hydration, compressing this mixture to form relatively large agglomerates, and comminuting these agglomerates to the desired grain size. A waterless production process, by compacting the bleach activator with at least one water-swellable auxiliary, without the use of water, is known from EP-A-0 075 818.
Disadvantages of these activator granules are that the properties of the granules are fixed essentially by the binder and by the granulating method used and that the resulting granules, besides the advantages described in the literature, often have certain disadvantages as well, for example suboptimal release of active substance, low abrasion resistance, high dust content, inadequate shelf life, separation within the powder or damage to the color of the fabric when used in detergents and cleaning materials.
In order to give granules defined properties a coating step is often carried out subsequent to the granulating step. Common methods are coating in mixers (mechanically induced fluidized bed) or coating in fluidized-bed apparatus (pneumatically induced fluidized bed).
For instance, WO 92/13798 describes, for a bleach activator, coating with a water-soluble organic acid which melts at above 30xc2x0 C. and WO 94/03305 describes coating with a water-soluble acidic polymer in order to reduce color damage to the laundry.
WO 94/26862 discloses the coating of granules consisting of bleach activator and a water- and/or alkali-soluble polymer with an organic compound melting at between 30 and 100xc2x0 C. for reducing separation in the pulverulent end product. In this case the activator granules are placed in a Lxc3x6dige plowshare mixer, circulated at from 160 to 180 rpm at room temperature, without using the pelletizer, and then sprayed with the hot melt. A disadvantage of this process is the very poor coating quality, which, although it brings about a reduction in separation in the pulverulent end product, has no effect on the other granule properties, such as release of active substance, abrasion resistance, dust content or shelf life, for example. The positive effect on the separation behavior can probably be attributed to a droplet-like solidification of the coating substance on the granule surface allowing the individual grains to hook together in the bulk product.
The object of the present invention was to develop a coating process for activator granules which makes it possible to tailor the granule properties within a wide range at the same time as making optimum use of the coating material.
This object was achieved by a thermal conditioning during and/or after coating.
The invention accordingly provides a process for producing coated bleach activator granules in which bleach activator base granules are coated with a coating substance and are simultaneously or subsequently thermally conditioned.
Base granules which can be used are all activators which in granulated form have a melting point of above 100xc2x0 C. Examples of activator substances are tetraacetylethylenediamine (TAED), tetraacetylglycoluril (TAGU), diacetyldioxohexahydrotriazine (DADHT), acyloxybenzenesulfonates (e.g. nonanoyloxybenzenesulfonate [NOBS], benzoyloxybenzenesulfonate [BOBS]), acylated sugars (e.g. pentaacetylglucose [PAG]) or compounds as are described in EP-A-0 325 100, EP-A-0 492 000 and WO 91/10719. Other suitable activators are N-acylated amines, amides, lactams, activated carboxylic esters, carboxylic anhydrides, lactones, acylals, carboxamides, acyllactams, acylated ureas and oxamides, and furthermore, especially nitriles, which in addition to the nitrile group may also contain a quaternized ammonium group. Mixtures of different bleach activators can also be present in the base granules.
These base granules can include the customary granulating auxiliaries, which should have a melting point of more than 100xc2x0 C. Suitable such auxiliaries are film-forming polymers, for example cellulose ethers, starch, starch ethers, homopolymers, copolymers and graft copolymers of unsaturated carboxylic acids and/or sulfonic acids and also the salts thereof, organic substances, for example cellulose, crosslinked polyvinylpyrrolidone, or inorganic substances, for example silicic acid, amorphous silicates, zeolites, bentonites, alkali metal phyllosilicates of the formula MMxe2x80x2SixO2x-1*yH2O (M,Mxe2x80x2=Na, K, H; x=1.9-23; y=0-25), orthophosphates, pyrophosphates and polyphosphates, phosphonic acids and their salts, sulfates, carbonates and bicarbonates, Depending on what is required these granulating auxiliaries can be employed as individual substances or as mixtures.
In addition to the bleach activator and the granulating auxiliary the bleach activator base granules may also include further additives which enhance properties such as, for example, shelf life and bleach activation. Such additives include inorganic acids, organic acids, for instance mono- or polybasic carboxylic acids, hydroxycarboxylic acids and/or ether carboxylic acids, and also salts thereof, complexing agents, metal complexes and ketones.
Depending on what is required, the abovementioned additives can be employed as individual substances or as mixtures.
The base granules are made by mixing a dry bleaching activator with a dry inorganic binder material, pressing this mixture to give relatively large agglomerates and comminution of these agglomerates to the desired particle size.
The ratio of bleaching activator to inorganic binder material is usually 50:50 to 98:2, preferably 70:30 to 96:4% by weight. The amount of additive depends in particular on its nature. Thus, acidifying additives and organic catalysts are added to increase the performance of the peracid in amounts of 0-20% by weight, in particular in amounts of 1-10% by weight, based on the total weight, while metal complexes are added in concentrations in the ppm range.
Suitable coating substances are all compounds or mixtures thereof which are solid at room temperature and which soften or melt in the range from 30 to 100xc2x0 C.
Examples of such are:
C8-C31 fatty acids (e.g. lauric, myristic, stearic acid): C8-C31 fatty alcohols; polyalkylene glycols (e.g. polyethylene glycols having a molar mass of from 1000 to 50,000 g/mol); nonionics (e.g., C8-C31 fatty alcohol polyalkoxylates with from 1 to 100 moles of EO); anionics (e.g., alkanesulfonates, alkylbenzenesulfonates, xcex1-olefinsulfonates, alkyl sulfates, alkyl ether sulfates having C8-C31 hydrocarbon radicals); polymers (e.g., polyvinyl alcohols); waves (e.g. montan waxes, paraffin waxes, ester waxes, polyolefin waxes); silicones.
Within the coating substance which softens or melts in the range from 30 to 100xc2x0 C. there may additionally be other substances, not softening or melting in this temperature range, in dissolved or suspended form, examples being polymers (e.g. homopolymers, copolymers or graft copolymers of unsaturated carboxylic acids and/or sulfonic acids and alkali metal salts thereof, cellulose ethers, starch, starch ethers, polyvinylpyrrolidone); organic substances (e.g., mono- or polybasic carboxylic acids, hydrocarboxylic acids or ether carboxylic acids having 3 to 8 C-atoms, and the salts thereof); colorants; inorganic substances (e.g., silicates, carbonates, bicarbonates, sulfates, phosphates, phosphonates).
Depending on the desired properties of the coated activator granules, the content of coating substance can be from 1 to 30% by weight, preferably from 5 to 15% by weight, based on coated activator granules.
The coating substances can be applied using mixers (mechanically induced fluidized bed) and fluidized-bed apparatus (pneumatically induced fluidized bed). Examples of possible mixers are plowshare mixers (continuous and batchwise), annular bed mixers or else Schugi mixers. If a mixer is used, the thermal conditioning can take place in a granule preheater and/or directly in the mixer and/or in a fluidized bed downstream of the mixer. The coated granules can be cooled using granule coolers or fluidized-bed coolers. In the case of fluidized-bed apparatus, the thermal conditional conditioning takes place by way of the hot gas used for fluidizing. The granules coated by the fluidized-bed method, as with the mixer method, can be cooled by way of a granule cooler or a fluidized-bed cooler. In both the mixer method and the fluidized-bed method the coating substance can be sprayed on by way of a single-substance or dual-substance nozzle apparatus.
The thermal conditioning comprises a heat treatment at a temperature from 30 to 100xc2x0 C. but not higher than the melting or softening temperature of the respective coating substance. It is preferred to operate at a temperature which lies just below the melting or softening temperature.
The grain size of the coated bleach activator granules is from 0.1 to 2.0 mm, preferably from 0.2 to 1.0 mm and, with particular preference, from 0.3 to 0.8 mm.
The precise temperature during thermal conditioning or the difference in temperature from the melting point of the coating substance is dependent on the amount of the coating material, on the thermal conditioning time and on the properties desired for the coated bleach activator granules, and must be determined in preliminary experiments for the particular system.
The period for thermal conditioning is from approximately 1 to 180, preferably from 3 to 60 and, with particular preference, from 5 to 30 minutes.
The advantage of the new process over the prior art is that the liquid coating material does not solidify too rapidly and thus has the possibility of running as a thin film over the surface of the granules. This produces a highly uniform coating of the grain in a thin layer with the coating substance, and an optimum coating effect for use of a minimum amount of coating substance. In conventional processes, i.e. those without a thermal conditioning step, solidification of the individual droplets on the cold granule surface is too rapid. Consequently, the surface is covered only with fine individual droplets and still has large coating voids. As a result, the desired coating effect is not fully obtained or a much higher amount of coating substance is required in order to obtain the desired coating effect. In the latter case, however, the content of activator substance is reduced, which in many cases is undesirable.
By means of the novel process it is possible to tailor the properties of the activator granules within broad ranges to the desired specifications by an appropriate choice of the coating substance, the coating rate and the process temperature regime. In this context it is possible in particular to optimize in a targeted manner the following activator granule properties.
1. Time-optimized release of active substance.
In order to avoid interaction between the bleaching system and the enzyme system it is advantageous to couple a slightly delayed reaction and active-substance release of the bleaching system with rapid enzyme action, in this way the enzymes can develop their washing power fully within the first few minutes of the washing process without being damaged by the bleaching system. Only after the enzymes have done their job is the bleaching process set in motion by reaction of the bleach activator with the hydrogen peroxide source. Appropriate coating of the bleach activator makes it possible to tailor the reactivity. i.e. the rate of dissolution or the rate of formation of the peracid, specifically to the enzyme system. The process permits controlled adjustment of the rate of formation of the peracid at the same time as having a minimal amount of coating substance and thus the maximum activator content.
2. Increasing the abrasion resistance
By coating granules with softening or melting substances it is possible to increase the abrasion resistance of activator granules. The increase in abrasion resistance is greater than better the coating of the granule surface with the coating substance. The novel coating process makes it possible, with a minimum coating rate, to bring about optimum flow of the coating substance over the granule surface and thus an optimum enhancement of the abrasion resistance.
3. Reducing the dust content
The novel coating process, in which excessively rapid solidification of the softening or melting coating substance is prevented by means of appropriate thermal conditioning during and/or after the coating step also makes it possible for granules to be dedusted in an optimum manner with a minimal coating rate, since the coating substance remains flowable and bindable over a relatively long period and is thus able to bind more dust particles. With prior art coating, on the other hand, there may at worst even be an increase in the dust content as a result of in some cases direct spray drying.
4. Extending the shelf life
When a detergent and cleaning material is stored there may be a reaction at the boundary between activator grain and a directly adjacent grain of the hydrogen peroxide source, with subsequent loss of active oxygen and thus uncontrolled breakdown of the bleaching system. By means of optimum coating, as is possible only through the novel coating process, a complete protective layer is constructed at the grain boundary, which layer then prevents reaction of the activator grain with the grain of the hydrogen peroxide source in the course of storage. When water-soluble and/or low-melting coating substances are used it is nevertheless possible to obtain the required bleaching performance in the washing process.
The granules obtained in this way are directly suitable for use in detergents and cleaning materials. They are ideal for use in heavy-duty detergents, scouring salts, dishwashing agents, general purpose cleaning powders and denture cleansers. In such formulations the granules of the invention are employed usually in combination with a hydrogen peroxide source. Examples thereof are perborate monohydrate, perborate tetrahydrate, percarbonates, and adducts of hydrogen peroxide with urea or with amine oxides. The formuation may also feature further, prior art detergent ingredients, such as organic or inorganic builders and cobuilders, surfactants, enzymes, washing additives, fluorescent whiteners and fragrance.